I was running into issues getting an API Token as well, albeit on a self-hosted install. I reached out to ActiveCollab support and they pointed me to a Getting Tokens for Cloud Instances.md gist which appears to have slightly different syntax with the use of a different endpoint and an "Intent" variable. Give that a look and see if it helps.
I was finally able to get an API Token with the following curl request
curl --location --request POST 'https://<URL-OF-SELF-HOSTED-VERSION>/api/v7/issue-token' \
--header 'Content-Type: application/json' \
--data-raw '{
"username": "<YOUR EMAIL HERE>",
"password": "<YOUR PASSWORD HERE>",
"client_name": "My Awesome App",
"client_vendor": "ACME Inc"
}'
Based on what their support folks said, you might have luck on the cloud version with the below, ensuring to add your account ID.
curl --location --request POST 'https://app.activecollab.com/<YOUR-ACCOUNT-ID>/api/v7/issue-token' \
--header 'Content-Type: application/json' \
--data-raw '{
"username": "<YOUR EMAIL HERE>",
"password": "<YOUR PASSWORD HERE>",
"client_name": "My Awesome App",
"client_vendor": "ACME Inc"
}'